Antibiotic susceptibility testing is a very important discipline used everywhere in hospitals, health clinics, medical production plants, food and drink production plants etc. The large number of different chemicals and standardized procedures and the enormous number of tests performed each year gives room for a huge industry benefitting of the micro organisms growing everywhere.
Some of the tests are indirect tests, i.e. measure or observe the presence of a derivate of microbial activity such as waste products or a redox indicator, instead of observing the microbial activity directly.
The costs of performing antibiotic susceptibility tests, e.g. in hospitals, are huge and growing continuously. Furthermore the long test incubation periods of up to 6 days pose a big problem, as treatments cannot await such long response times. The patient may be dead when the result is ready. Physicians thus often prescribe broad band antibiotics in order to start treatment immediately before results arrive. Faster results (within a few hours) may enable the use of narrow band antibiotics targeted directly at the cause of the disease, thereby minimizing the risk of creating resistance to antibiotics in general.
One of the most common susceptibility tests performed is testing urine for urinary tract infections (UTI). Urine is a very good growth medium in itself, and utmost care must be taken not to contaminate the urine with bacteria during urine sample handling. Furthermore it is necessary to start the testing in the laboratory within 1-2 hours if the reliability of the test results shall remain unaffected. In order to reduce the costs in health care systems, many small laboratories have been closed leaving only a few large laboratories often situated at hospitals. The urine sample must thus arrive at the central laboratory within 1-2 hours, which is not a problem at major hospitals, but when the sample is acquired at the GP the distance and transport time to the laboratory can be a problem. In these cases it may be necessary to refrigerate the urine samples and keep them in special containers until arrival at the laboratory. Even in hospitals where the laboratory may be in close proximity, it is beneficial to start a susceptibility testing immediately after sample acquisition, since this minimizes the test result delivery time. It is therefore desirable to have a small and easy-to-use apparatus for performing the susceptibility testing locally at the point of care.
Susceptibility testing of micro organisms comprises several levels of testing. One level may be to determine the types of micro organisms present in a sample, e.g. be bacteria, fungi, protozoa, algae or virus. Another level in the testing is to establish which type of antibiotic to be used for eliminating the micro organisms. The types of antibiotics may comprise narrow and broad spectre antibiotics as well as more specialised types. Similarly, tests may determine the best medication of the same type but from different producers.
Furthermore, it may be relevant to test the response of the micro organisms to different environments, such as aerobe and anaerobe, and in some cases even in phosphoric environments. Some situations may require testing the effect different levels and combinations of nutrition, especially when searching for specific types of micro organisms.
When the best antibiotic for destroying the micro organisms has been determined, it is important to determine the antibiotic concentration to be prescribed. Usually at least 5 different concentrations are tested, and up to 15 or more different concentrations may be used for determining the optimal concentration. The result of the concentration testing may be the MIT—Minimum Inhibitory Concentration, which indicates the concentration of the antibiotic necessary to prevent the micro organisms to grow. If concentrations below the MIT are used, the antibiotic will only eliminate some of the micro organisms, with the consequent risk of the remaining micro organisms to develop resistance or susceptibility toward the antibiotic.
Typically test results are formulated by categorizing the antibiotic candidates into Resistant, Intermediate or Susceptible.
Present test methods require the use of a large number of different chemicals and standardized procedures. The standards in US are maintained by CLSI (Clinical and Laboratory Standards Institute). The standards describe test details such as how to set up tests, including inoculation (concentrations), isolation distances, temperatures, inspection of growth results, incubation periods. Tests incubation periods may vary from a few hours (e.g. 16-24 hours) to several days (e.g. 3-6 days).
Often a 3 step method is used during incubation of the microorganisms. The first step is to incubate the primary culture. When a sufficiently high quality of the culture has been obtained, one or more monocultures are selected and isolated. The monocultures are then incubated again to obtain a sufficiently large amount of microorganisms for the last step—to incubate the microorganisms in Petri dishes or similar comprising different types and concentrations of antibiotics. The three steps is usually performed by hand and is thus expensive in manpower, and the time from the acquisition of the primary culture to the susceptibility testing may start is often many hours or several days.
The described complexity of susceptibility testing indicates the advantages of an apparatus that reduces the test time from many hours at the best to only few hours or even minutes. Furthermore, it would be advantageous to use more automated test procedures than is seen today, minimizing manual handling in laboratories. Finally, a cost reduction per test would obviously be of great benefit to all parts of the health care system.
Different solutions have been provided to overcome at least partly some of the problems described above.
One such solution is U.S. Pat. No. 6,153,400 Device and method for microbial antibiotic susceptibility testing by Matsumura et al. Matsumura provides a method and apparatus for performing microbial antibiotic susceptibility testing including disposable, multi-chambered susceptibility plates and an automated plate handler and image acquisition and processing instrument. The susceptibility plates are inoculated with a microorganism and anti-microbial agent(s) are applied such that the microorganism is exposed to a variety of concentrations, or a gradient of each anti-microbial agent. The plates are then placed in the instrument, which monitors and measures the growth of the microorganisms. This data is used to determine the susceptibility of the microorganism to the antibiotics. Such a system automates antimicrobial susceptibility testing using solid media and Kirby-Bauer standardized result reporting. The system is partly automatic, but handles agar disks for diffusion tests.
Another approach is shown in U.S. Pat. No. 4,448,534 Antibiotic susceptibility testing by Wertz et al. An apparatus is provided for automatically scanning electronically each well of a multi-well tray containing many liquid samples. A light source, preferably a single source, is passed through the wells to an array of photosensitive cells, one for each well. There is also a calibrating or comparison cell receiving the light. Electronic apparatus reads each cell in sequence, quickly completing the scan without physical movement of any parts. The resultant signals are compared with the signal from the comparison cell and with other signals or stored data and determinations are made and displayed or printed out. Thereby such matters as minimum inhibitory concentrations (MIC) of drugs and identification of microorganisms may be achieved. The apparatus according to U.S. Pat. No. 4,448,534 does not acquire an optical sectioning of said biological organisms.
Yet another system is filed as US patent application US 2005/0068614. A microscope system has a stage on which an observation sample including an observation object and a transparent member is to be placed, an objective lens which is placed to face the observation sample placed on the stage, a focusing unit which moves at least one of the stage and the objective lens to perform focusing operation, and an autofocus unit which controls a focusing driving unit by a so-called TTL system. After autofocus is performed for the transparent member by the autofocus unit, the focusing driving unit makes at least one of the stage and the objective lens move by a predetermined constant amount. The apparatus according to US patent application US 2005/0068614 does not acquire an optical sectioning of said biological organisms.